[Pkg-exim4-users] rejected RCPT Unrouteable address

[James Nightly]

I'm trying to setup Exim4 with Mailman. I'm on Debian testing. I have
router and everything setup according to the excellent Exim how-to.
The server can send messages, but if I reply to the sender the error
logs shows Unrouteable address. I'm using split configuration file.

exim4 -bt mailman at lists.myschool.org
R: system_aliases for mailman at lists.myschool.org
mailman at lists.myschool.org is undeliverable: Unrouteable address